Thrips off to big start in Virginia, North Carolina

• Our region has earned the distinction of having the highest levels of thrips and greatest potential damage to seedling cotton of anywhere in the U.S.

• As if our high thrips populations weren’t enough, our often cool spring conditions can limit early plant growth, exposing the susceptible cotyledon to two or three true leaf stage seedlings to thrips for extended periods.

• Thrips damage at this growth stage can result in significant yield losses and maturity delays.

With our exceptionally warm winter and good moisture levels, at this point it looks like thrips flights into cotton should be both large and early this year.

As most cotton producers in our area know from experience, the upper Southeast cotton production region could be designated as ‘Thrips Central’ for the Cotton Belt.

Our region has earned the distinction of having the highest levels of thrips and greatest potential damage to seedling cotton of anywhere in the U.S.

In some tests, with the help of a microscope, we sometimes count as many as 200 to 500 immature thrips per 5 seedlings! That’s a “ton” of thrips, especially if seedlings are unprotected. So it’s probably not a surprise that Virginia and North Carolina have the highest ratio of surrounding host vegetation to small average cotton field size.

As if our high thrips populations weren’t enough, our often cool spring conditions can limit early plant growth, exposing the susceptible cotyledon to two or three true leaf stage seedlings to thrips for extended periods. Thrips damage at this growth stage can result in significant yield losses and maturity delays.

Unfortunately, our often cool wet seedling grow off conditions, coupled with the very high ratio of thrips host acreage to small average cotton field size, often seems to create a ‘perfect storm’ of thrips headaches, especially on early planed cotton.

In a series of 80 or so replicated tests conducted here and in Virginia during the past decade, untreated cotton lost an average of approximately 250 pounds of lint to thrips damage compared to the best at-planting treatments. That’s a lot of cotton lost to such a tiny insect.

Until the availability of the aldicarb Temik-like replacement Meymik arrives in 2013 (by no means certain), our common default approach will likely remain the use of a seed treatment with a follow-up spray targeted at the early first true leaf stage.

Most producers up our way would judge this treatment combination to be only fair, as high thrips levels and less than ideal growing conditions on April to approximately May 10 planted cotton can result in stunted cotton and yield losses.

In 2011, however, we had a few consultants who scouted seedling cotton carefully twice per week and didn’t recommend a foliar spray in some fields. Unfortunately, scouting cotton this closely is an exception.

Over the past eight years, more than 85 percent of our cotton acreage has been over-sprayed following a seed treatment.

Foliar treatment needed

With the potential for thrips damage lasting up to 5 or 6 weeks after planting and seed treatments varying from about 2 to 3 weeks in their activity, a high percentage of foliar follow-up treatments for thrips is not surprising.

Although every year brings somewhat different, typically higher, rates of active ingredient to seed treatments, a look at the nicotinoids and their rates on seed suggest their performance against thrips should be similar. And that’s indeed the case.

Even back in the days when only Cruiser and Gaucho were available, many replicated tests suggested that these materials were essentially identical in their thrips activity — although many producers had their favorite.

Today, with insecticide plus nematicide plus extra fungicide on most seed treatments, recent tests in our area suggest that these combined seed treatments are similar in their activity against thrips, nematodes and diseases.

What’s new on the horizon?

• The Holy Grail of seed treatments would be a high rate (or new active ingredient) of an insecticide on cotton seed that would remain active for four to five weeks.

In many cases, our 3 weeks’ seed treatment activity seems to come up short by only a week or two.

So far, with the exception of a few testimonies to the contrary, this seemingly simple answer to short-lived seed treatment activity has defied the best efforts of major seed companies, consultants and university scientists.

Several high rate options will be evaluated here and elsewhere in 2012.

Another option will be the presence of multiple insecticides and nematicides on the same seed. One example for 2012 will be the Aeris/Poncho/VOTiVO option containing two nicotinoids and two nematicides, one conventional and biological. Whether these and other formulations will offer extended activity for thrips will be addressed in the coming year(s).

• In-furrow sprays with “new” materials showed some promise in North Carolina and Virginia in 2011. Although our data should be considered preliminary, Admire Pro (imidacloprid) showed extended activity against thrips in a test in Wilson County, North Carolina and in testing at the Tidewater Ag. Research and Extension Center in Virginia This and additional products will be evaluated more widely in 2012.

• Although approved for a federal label in December 2011 the introduction of the aldicarb-based, Temik-like product Meymik will likely face further obstacles before being available to cotton producers, possibly by 2013.

Probably produced, formulated and shipped from China, little is known about the possible costs, flowability and efficacy of Meymik.

Additionally, the successful re-registration of aldicarb (a carbamate), the active ingredient, by the EPA in 2014 or 2015 is not a given.

As part of a Southeast Cotton Working Group initiative, Cotton Incorporated has sponsored a series of tests which evaluated new and standard foliar insecticides for thrips control in Virginia, North Carolina, South Carolina, Georgia and Alabama.

Two insecticides, Radiant and Benevia, showed thrips control on a par with acephate (Orthene and other brand names).

We and others have confirmed that the combination of Orthene following a seed treatment greatly increases the odds of having to treat later for cotton aphids and spider mites.

Radiant and Benevia will likely be significantly less disruptive against beneficial insects.

The major downside of these materials is their prohibitive $20-$30 per acre cost at the rates tested.

This year’s series of tests in our region will evaluate the effectiveness of several rates of these insecticides in the hope that one or both may give us an additional tool in minimizing our annual thrips dilemma.

In essentially all of our research trials, when the cotton plants have an average of approximately 5 true leaves with adequate moisture levels and reasonably warm weather, thrips control was no longer needed.

Our best outcome for a reasonable “thrips season” would be warm moist conditions conducive to rapid seedling growoff — and perhaps a few more mid-May cotton planting dates.